Interpretive Summary: Dietary guidelines for physical activity recommend 30 minutes a day most days of the week. But for overweight and obese people more physical activity is recommended in order to reduce body weight. Some people go to extreme levels of physical activity and participate in ultra-endurance events that last more than 24 hours. The body composition of individuals participating in these ultra-marathon events can have substantial impact their success in completing the event and may vary widely. We evaluated the body mass index (BMI) and body fat of participants in a 100 mile ultra-marathon. The run started on a Saturday at 6am and ended at noon on Sunday; a total of 30 hours. We found that there was a wide range of variation in BMI and body fat in both the men and women participants. BMI for men ranged from 19 to 32; a value of 25 or more is considered overweight and 30 or more is defined as obese. BMI for women ranged from 18 to almost 27. However, BMI measurements do not acturately reflex body fat levels and can therefore be misleading. The average body fat for the men that participated in the 100 mile race was 17% and for the women 26%. Among the men there was a significant relationship between body fat and finish time; participants that successfully completed the 100 miles within 30 hours had less body fat than the participants who did not complete the 100 miles. No relationship was found between finish time and body fat for the women. Despite the wide range of BMI and body fat among the ultra-marathon participants, faster men had lower body fat values than slower men and those that did not finish. The number of women participants in this event was fewer than the men and limited our ability to find important associations that may have contributed to the successful completion of ultra-marathon event. The wide range in BMI and body fat of these participants suggest that exercising more than 30 minutes a day may not always result in lower BMI or body fat.

Technical Abstract:
This study compares body composition characteristics with performance among participants in a 161-km trail ultramarathon. Height, mass, and percent body fat from bioimpedence spectroscopy were measured on 72 starters. Correlation analyses were used to compare body characteristics with finish time, and unpaired t-tests were used to compare characteristics of finishers with non-finishers. Mean (±SD) BMI (kg•m-2) was 24.8±2.7 (range 19.1-32.2) for the men and 21.2±2.1 (range 18.1-26.7) for the women. Among the four fastest runners, BMI values range from 19.5 to 23.4 for men and 18.1 to 22.9 for women. Mean (±SD) percent body fat values for men and women were 17±5 (range 5-35) and 21±6 (range 10-29), and ranged from 6 to 14 and 14 to 27 among the fastest four men and women. There was a significant positive correlation (p=0.0025) between percent body fat and finish time for men but not for women, and percent body fat values were lower for finishers than non-finishers for men (p=0.03) and women (p=0.04). We conclude that despite wide variations in BMI and percent body fat among ultramarathon participants, the faster men have lower percent body fat values than the slower men, and finishers have lower percent body fat values than non-finishers.